You are a scientist and have created this shrinking serum. Your girlfriend wants you to use it on yourself but you are too nervous and afraid to. She slips it into your coffee though and tells you she will watch over you and you both can have some fun while you shrink down. You start to get really horny as that is a side effect and shrink down several inches. Your clothes start to fall off and your girlfriend giggles at you because your cock has also shrunk. She teases you about the size shrink a little bit but tells you that 4in isn’t that bad for a cock. She jerks you off and each time you cum you shrink a little bit more and she teases you even more but she still wants to jerk you off. When you get to shin level you then get to eat her out and as you shrink to 6in she uses you as a dildo to pleasure herself.